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(11) | EP 3 029 682 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | A METHOD FOR OPERATING A CONDUCTIVE BRIDGING MEMORY DEVICE |
| (57) A method is disclosed for operating a Conductive Bridge Random Access Memory (CBRAM)
device (1), comprising an electrolyte element (2) sandwiched between a cation supply
top electrode (3) and a bottom electrode (4). The method comprises: conditioning the
CBRAM device (1) by applying a forming current pulse having a pulse width (tf) of 100ns or less and a pulse amplitude (If) of 10uA or less, and when programming, setting the conditioned CBRAM device (1)
to a Low Resistance State (LRS) by applying a set current pulse having a pulse width
(ts) of 100ns or less and a pulse amplitude (Is) equal to or larger than the forming
current pulse amplitude (If).
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Field
[0001] The present disclosure relates to resistive-switching Random Access Memory (RRAM) devices, in particular to Conductive Bridging Random Access Memory devices, also known as CBRAM devices. In particular the method relates to a method for operating such conductive bridging memory device.
State of the art
[0002] The Conductive Bridging Random Access Memory (CBRAM) device is considered as a valuable non-volatile storage technology. It offers high endurance, reduced variability and good scalability.
[0003] A CBRAM device contains an insulating layer sandwiched between an active top electrode providing metal cations, e.g. Cu+ or Ag+, and an inert bottom electrode, i.e. which doesn't provide such metal cations. The operation of the CBRAM device relies on the voltage-induced redox-based formation and rupture of a metal-based, e.g. Cu or Ag, conductive filament (CF) in the insulating layer acting as a solid state electrolyte.
[0004] When an electrical field is applied between both electrodes, metal cations provided by the active top electrode will drift towards the opposite inert bottom electrode through the insulating layer thereby forming the conductive filament. As a result, during operation, the CBRAM device can be reversible switched between a high resistive (HRS) or reset state and a low resistive (LRS) or set state.
[0005] After manufacturing the CBRAM device and before putting it into operation, a forming step is applied to each CBRAM device to create an initial conductive filament therein. Such a forming step requires a current pulse having a long pulse width and a large pulse height, typically more than 50uA during 1 second or more. These forming conditions turns the forming step into a time-consuming process.
[0006] In addition, the current conditions of this forming step determines the programming current conditions, as typically the same high current level is used for forming as well as for programming to improve the memory window of the CBRAM device, i.e. the difference in resistance between the reset and set state.
[0007] These current conditions will also determine the feasibility of using CBRAM as a replacement for flash memory device, requiring both fast programming times, low forming/programming current densities and a sufficient memory window.
[0008] Hence, there is a need for a CBRAM device that doesn't suffer from one or more of the above shortcomings of the state-of-the-art CBRAM devices.
Summary
[0010] A method is disclosed for operating a memory comprising at least one Conductive Bridge Random Access Memory (CBRAM) device, the memory device comprising an electrolyte element sandwiched between a cation supply top electrode and an inert bottom electrode. The operating method comprise conditioning the memory device by applying a forming current pulse a pulse amplitude (If) of 10uA or less. Preferably the pulse amplitude (If) is 1uA or less. Preferably the forming current pulse has a pulse width (tf) of 100ns or less.
[0011] The memory can comprise an array of the memory device, whereby the memory devices in the array are conditioned in parallel.
[0012] The conditioned memory device is set to a Low Resistance State (LRS) by applying a set current pulse having a pulse width (ts) of 100ns or less and a current pulse amplitude (Is) equal to or higher than the forming current pulse amplitude (If). Preferably the set current pulse amplitude (Is) is above 10ua.
[0013] The set current pulse amplitude (Is) can be determined in view of a Low Resistance State selected from a set of Low Resistance States, thereby allowing multilevel programming.
[0014] The cation supply electrode of the memory device preferably comprises copper or silver. The bottom electrode of the memory device preferably comprises tungsten or titanium-nitride. The electrolyte element of the memory device preferably comprises alumina-oxide, silicon-oxide, tungsten-oxide, silicon-nitride, or a combination thereof.
Brief description of the figures
[0015] For the purpose of teaching, drawings are added. These drawings illustrate some aspects and embodiments of the disclosure. They are only schematic and non-limiting. The size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the disclosure. Like features are given the same reference number.
FIG 1 illustrates a CBRAM device according to the disclosure.
FIG 2 illustrates a forming and set programming step according to the disclosure.
Fig 3 illustrates the impact of the amplitude (Is) of the set current on the Low Resistive State (LRS) and on the High Resistive State (HRS) state.
Detailed description
[0016] The present disclosure will be described with respect to particular embodiments and with reference to certain drawings but the disclosure is not limited thereto. Furthermore, the terms first, second and the like in the description, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the disclosure described herein are capable of operation in other sequences than described or illustrated herein. Moreover, the terms top, under and the like in the description are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the disclosure described herein are capable of operation in other orientations than described or illustrated herein.
[0017] The present disclosure relates to the forming of a CBRAM device using a forming current pulse of lower width (tf) and height (If), which reduces the time required to condition a pristine CBRAM device. As this programming current (If) is reduced, multiple pristine CBRAM (1) devices can be conditioned in parallel. Typically this parallel conditioning of an array of CBRAM (1) devices is executed while the pristine memory devices (1) are still on the wafer. After being conditioned, the wafer is diced into memory chips. The diced memory chip containing the array of conditioned memory devices (1) is packaged while the Low Resistance State (LRS) or set state of the packaged and conditioned memory device (1) is essentially unaffected by this packaging process.
[0018] Such CBRAM device (1) is illustrated in FIG 1. Here a Conductive Bridge Random Access Memory (CBRAM) device (1) is shown comprising an insulating electrolyte element (2) sandwiched between a cation supply top metal electrode (3) and an inert bottom electrode (4). The bottom electrode (4) is labelled 'inert' as it doesn't provide cations during the filament forming process.
[0019] As discussed in the following paragraphs, the CBRAM device (1) is preferably formed using materials and methods compatible with CMOS processing. This compatibility allows integration of the CBRAM device (1) on a CMOS substrate, i.e. a semiconductor substrate comprising logic devices, such as field effect transistors, for controlling the operation of the memory device (1).
[0020] Preferably, the dielectric material (5) of the electrolyte element (2) is selected from the group of alumina oxides, hafnium oxides, tantalum oxides, silicon oxides, tungsten oxides, silicon nitrides, or a combination thereof.
[0021] The cation supply electrode (3) can comprise Cu or Ag, supplying respectively Cu+ and Ag+ cations during programming. Preferably the cation supply electrode (3) is a Cu alloy, such as Cu-Te, Cu-Ge, Cu-Ge-Te, Cu-Te-C, Cu-Ti.
[0022] Optionally a metallic liner (not shown) is formed, separating the cation supply electrode (3) from the electrolyte element (2). In case a Cu or Ag containing top electrode (3) is formed, this metallic layer contains Ta or TiW.
[0023] Typically the bottom electrode (4) comprises tungsten. Preferably the bottom electrode (4) is formed of tungsten or titanium-nitride, e.g. TiN.
[0024] When biasing (V+-V-) the top electrode (3) positive with respect to the bottom electrode (4) of such a CBRAM device (1), an electrical field is applied over the electrolyte element (2). A conductive filament (not shown) then grows (9) from the cation supply metal top electrode (3) towards the bottom dielectric layer (7) due to cation reduction, M+ -> M, within the electrolyte element (2).
[0025] Such a pristine Conductive Bridge Random Access Memory (CBRAM) device (1) is conditioned, i.e. an initial conductive filament is formed, by applying a forming current pulse having a pulse amplitude (If) of 10uA (micro-Ampere) or less, preferably 5uA or less, more preferably 1uA or less whereby the pulse amplitude is higher than zero.
[0026] If the electrolyte element (2) comprises or consist of silicon-oxide, or tungsten oxide, the amplitude of the forming current (If) can be 5uA or less.
[0027] Preferably the forming current pulse has a pulse width (tf) of 100ns (nanoseconds) or less, preferably 50ns or less whereby the pulse width is higher than zero. In case an array of such memory devices (1) is conditioned, the memory devices (1) in the array can be conditioned in parallel instead of sequentially, thereby increasing the throughput of the conditioning step.
[0028] A memory device (1), conditioned as discussed in the foregoing paragraphs using a short current forming pulse, can then be programmed. When setting this memory device (1), i.e. bringing it into a Low Resistive State (LRS), a set current pulse is applied. This set current pulse has a pulse width (ts) of 100ns or less, but higher than zero, preferably 50ns or less, whereby its current pulse amplitude (Is) is equal to or higher than the amplitude (If) of current pulse applied to form this memory device (1). Preferably this set current pulse amplitude (Is) is above 10uA. Fig 2 illustrates the relative amplitudes of the forming and set current pulse according to this disclosure.
[0029] The amplitude (Is) of this set current pulse now differs from the amplitude (If) of the forming current pulse. Hence, one can select the set current pulse amplitude (Is) in view of the resistance value desired in the Low Resistive State (LRS). As illustrated in Fig 3, two values for this amplitude were applied (Is = 10uA or 50uA). This difference in set current pulse amplitude (Is) only had limited impact on the resistance value obtained during the subsequent High Resistive State (HRS). The corresponding resistance value of the LRS was noticeably shifted to lower values when increasing the set current pulse amplitude (Is). The memory window (MW), even at 10uA, still allows distinguishing the Low Resistive State from the High Resistive State. Preferably the amplitude of the set current pulse is above 10uA and below 500uA, more preferably above 10uA and up to and including 50uA.
[0030] As this set current pulse amplitude (Is) can be selected substantially independently from the resistance value of the HRS and of the forming state, with the limitations discussed above, one can program the memory device (1) to different low resistance levels in the LRS depending on the set current pulse amplitude (Is) applied. The current disclosure thus allows multilevel cell programming, whereby the set current pulse amplitude (Is) is determined in view of a Low Resistance State selected from a set of Low Resistance States.
[0031] Although, the set current pulse amplitude ((Is) is preferably selected to be equal to or higher than the amplitude (If) of the current pulse applied to form this memory device (1), one can apply a current pulse amplitude lower than this forming current pulse amplitude. Such a lower set current pulse amplitude results in a higher value of the Low Resistive State as illustrated by FIG 3. This broadens the range of the set current amplitude from which to select in order to reversibly switch between different values of the Low Resistive State.
1. A method for operating a memory comprising at least one Conductive Bridge Random Access
Memory (CBRAM) device (1), the memory device comprising an electrolyte element (2)
sandwiched between a cation supply top electrode (3) and an inert bottom electrode
(4), the method comprising:
conditioning the memory device (1) by applying a forming current pulse having a pulse amplitude (If) of 10uA or less.
2. The method of claim 1, wherein:
the pulse amplitude (If) is 1uA or less.
3. The method of claim 1 or 2, wherein:
the forming current pulse has a pulse width (tf) of 100ns or less.
4. The method of any of the foregoing claims, wherein:
the memory comprises an array of the memory device (1),
whereby the memory devices (1) in the array are conditioned in parallel.
5. The method of any of the foregoing claims, further comprising:
setting the conditioned memory device (1) to a Low Resistance State (LRS) by applying a set current pulse having a pulse width (ts) of 100ns or less and a current pulse amplitude (Is) equal to or higher than the forming current pulse amplitude (If).
6. The method of any of the foregoing claims, wherein:
the set current pulse amplitude (Is) is above 10ua.
7. The method of any of the claims 1 to 4, wherein:
the set current pulse amplitude (Is) is less than the forming current pulse amplitude (If).
8. The method of any of the foregoing claims, further comprising:
determining the set current pulse amplitude (Is) in view of a Low Resistance State selected from a set of Low Resistance States.
9. The method of any of the foregoing claims:
the cation supply electrode (3) comprises copper or silver.
10. The method of any of the foregoing claims, wherein:
the bottom electrode (4) comprises tungsten or titanium-nitride.
11. The method of any of the foregoing claims, wherein:
the electrolyte element (2) comprises alumina-oxide, silicon-oxide, tungsten-oxide, silicon-nitride, or a combination thereof.